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1989 (1)
1Author    Guogang Liang, NicolasA. Corfù, Helmut SigelRequires cookie*
 Title    Influence of Decreasing Solvent Polarity (Dioxane-Water Mixtures) on the Stability of Metal Ion Complexes Formed with Phosphate Monoesters  
 Abstract    The acidity constants o f H (R —M P)~, where R —M P: = 4-nitrophenyl phosphate (N PhP2). phenyl phosphate (PhP2) and D -ribose 5'-m onophosphate (R ibM P2). and the stability constants of the binary C u (R -M P) com plexes w'ere determ ined by potentiom etric pH titrations in aqueous solution and in 20. 30, 40 and 50% (v/v) dioxane-water mixtures. The solvent influence on the corresponding equilibrium constants is com pared with the same influence on previously studied systems containing uridine 5'-triphosphate. formate or acetate. The influence o f the solvent com position on the various ligand (L) system s was evaluated by constructing log Km(L) versus pK[j(L) plots; in all cases straight lines are obtained with slopes close to 1. This indicates that in all these system s, despite the different negative charges o f the involved ligands, the solvent effect on proton binding and on metal ion binding is approxim ately o f the same size: A decreasing solvent polarity resulting from the addition o f increasing am ounts o f organic solvent to the aqueous solutions favors the affinity o f the negatively charged ligands for protons and metal ions as well. Information o f this type is considered important because the 'effective' or 'equivalent solution' dielectric constants in active-site cavities o f enzym es are reduced com pared with the dielectric constant o f bulk water; i. e., in protein cavities also a decreased 'solvent polarity' is occurring and this is expected to affect the stability o f metal ion-ligand bonds. 
  Reference    Z. Naturforsch. 44b, 538 (1989); received N ovem ber 28 1988 
  Published    1989 
  Keywords    Phosphate M onoester, Metal Ion C om plexes, Solvent Influence, Stability Constants, A ctive-Site Cavities o f Enzymes 
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 TEI-XML for    default:Reihe_B/44/ZNB-1989-44b-0538.pdf 
 Identifier    ZNB-1989-44b-0538 
 Volume    44